Understanding Glycemic Load

The Glycemic Load is the most practical way to apply the Glycemic Index to dieting, and is easily calculated by multiplying a food's Glycemic Index (as a percentage) by the number of net carbohydrates in a given serving. Glycemic Load gives a relative indication of how much that serving of food is likely to increase your blood-sugar levels.

As a rule of thumb, most nutritional experts consider Glycemic Loads below 10 to be "low," and Glycemic Loads above 20 to be "high." Because Glycemic Load is related to the food's effect on blood sugar, low Glycemic Load meals are often recommended for diabetic control and weight loss.

Note: For a more extensive discussion of Glycemic Index and Glycemic Load, please see ND's Glycemic Index page.

Limitations to Glycemic Load's Use

To calculate Glycemic Load, you must first determine the food's Glycemic Index (GI), which can only be done via human testing. GI testing is relatively expensive and very time-consuming. Human test subjects are required, and only a limited number of laboratories currently perform these tests. Consequently, GI data is only available for a very small percentage of the foods that we consume.

The most prolific GI testing laboratory is based in Australia, so a large portion of the currently tested foods are of Australian origin. This further limits the usability of the data, because some of the tested foods do not have equivalent forms in the U.S. or other parts of the world.

To make matters worse, food manufacturers are creating new food products at a much faster rate than GI testing can be performed. Each year, tens of thousands of new packaged-food items are added to grocery shelves, but only a few hundred foods are tested for GI. Because of this, it's doubtful that we'll ever reach a point in time where GI is known for all foods.

In addition to these limitations, there is no recognized method for accurately determining GI for recipes, other than to submit the prepared recipe for the previously described human tests. The consequence of this is that a chef or home cook has no practical way to determine the Glycemic Index or Glycemic Load for any of his own creations.

Clearly, what is needed is a way to estimate Glycemic Load when Glycemic Index is unknown.

Extending Glycemic Load with Estimated Values

By doing a multivariate analysis on the existing glycemic data, Nutrition Data was able to create a mathematical formula that estimates Glycemic Load by comparing the food's levels of commonly known nutrients. This formula was not intended to completely replace traditional Glycemic Load calculations, but it does produce a reasonable estimation when a food's Glycemic Index is unknown.

Below is a graph that displays a comparison between actual and estimated Glycemic Loads for over 200 common carbohydrate-containing foods.

DiscussionIn the above graph, each blue diamond represents the measured Glycemic Load for a particular food. The black line represents the Estimated Glycemic Load (eGL)™ produced by Nutrition Data's mathematical formula. For this study, Glycemic data was taken from the International table of glycemic index and glycemic load values: 2002 for those foods that could most reliably be matched to existing entries in Nutrition Data's database. For each food considered by this study, Nutrition Data used a serving size of 100 grams. The mean GL for foods in this study was 20.8, and the resulting eGL formula had a standard error of 5.5.

Benefits of eGLThe average diet contains many foods for which Glycemic Index values have not yet been determined. By using eGL to estimate Glycemic Loads for these foods, you receive more complete dietary feedback than if the effects of such foods were simply ignored.

Estimated Glycemic Load (eGL)™ on Nutrition Data

Estimated Glycemic Loads appear on Nutrition Data's Nutrition Facts pages, and have a format similar to the example on the right:

The Estimated Glycemic Load was approximated by comparing this food's nutrient profile to that of similar foods for which glycemic values have been measured.

Because Glycemic Load is dependent on serving size, you'll see the eGL value change if you change the serving size in the Serving Size drop-down at the top of the Nutrition Facts page.

A composite eGL is also included on your My Tracking report. This composite eGL is the sum of eGLs for all foods in your running total, and provides feedback for diets that recommend limiting total daily Glycemic Load.

Note: For more information on the Glycemic Index values generated at the University of Sydney, Australia, please see GlycemicIndex.com.